#include<bits/stdc++.h>
#define fi first
#define se second
#define mk make_pair
#define pub emplace_back
#define pob pop_back
using namespace std;
const int N=5010;
typedef long double ld;
int n;ld a,s[N],rg[N][2];
ld dp[N][2];
ld solve(ld x,ld y,ld z){
	if(y*y-4*x*z<0) return -1e9;
	return (-y+sqrt(y*y-4*x*z))/(2*x);
}
bool check(int st,int ed,ld v0,ld bas){
	for(int k=st+1;k<=ed;k++){
		ld tt=solve(a/2,v0,s[st]-s[k])+bas;
	//	cout<<st<<"->"<<ed<<":"<<k<<" "<<tt<<endl;
		if(rg[k][0]>tt||rg[k][1]<tt) return 0;
	}
	return 1;
}
int main(){
//	auto file1=freopen("dd.in","r",stdin);
	cin>>n>>a;n++;
	for(int i=1;i<=n;i++) cin>>s[i];
	for(int i=1;i<=n;i++) cin>>rg[i][0]>>rg[i][1];
	dp[1][0]=dp[1][1]=0;
	ld ans=1e12;
	for(int i=2;i<=n;i++){
		for(int opi=0;opi<=1;opi++){
			dp[i][opi]=-1e9;
			for(int j=1;j<i;j++){
				for(int opj=0;opj<=1;opj++){
					if(dp[j][opj]<0) continue;
					ld tl=rg[j][opj],tr=rg[i][opi];
					ld x=s[i]-s[j];ld t=sqrt(x*2/a);
					if(t<=tr-tl){
						bool ok=1;
						for(int k=j+1;k<i;k++){
							ld tt=sqrt(2*(s[k]-s[j])/a)+tr-t;
							if(rg[k][0]>tt||rg[k][1]<tt){
								ok=0;
								break;
							}
						//	cout<<j<<" "<<k<<" "<<i<<" "<<tt<<endl;
						}
						if(ok) dp[i][opi]=max(dp[i][opi],t*a);
					}else{
						ld v0=(x-(tr-tl)*(tr-tl)/2*a)/(tr-tl);
						if(v0>=0&&v0<=dp[j][opj]&&check(j,i-1,v0,rg[j][opj])){
							dp[i][opi]=max(dp[i][opi],2*x/(tr-tl)-v0);
						}
					}
				}
			}
		//	cout<<i<<","<<opi<<":"<<dp[i][opi]<<endl;
			if(dp[i][opi]<0) continue;
			if(i==n) ans=min(ans,rg[i][opi]);
			else{
				ld v=dp[i][opi];
				if(check(i,n,v,rg[i][opi])){
					ld tt=solve(a/2,v,s[i]-s[n]);
			//		cout<<"suc:"<<i<<" "<<v<<" "<<rg[i][opi]<<"+"<<tt<<endl;
					ans=min(ans,rg[i][opi]+tt);
				}
			}
		}
	}
	printf("%0.5Lf",ans);
	return 0;
}